whAt ConClusion CAn BE DrAwn From thE sCiEntists' oBsErvAtion
A．insECts hAvE DEvElopED somE sort oF rEsistAnCE to mAn-mADE poisons.
B．insECts hAvE BEEn EAting plAnts For ABout 250 million yEArs.
C．FArmErs somEtimEs usE A ComBinAtion oF two or thrEE insECtiCiDEs At onCE.
D．nEw insECts mAtE with insECts whiCh survivED From A CErtAin kinD oF insECtiCiD